Some vehicle engine systems utilize both direct in-cylinder fuel injection and port fuel injection. The fuel delivery system may include multiple fuel pumps for providing fuel pressure to the fuel injectors. As one example, a fuel delivery system may include a lower pressure fuel pump (or lift pump) and a higher pressure (or direct injection) fuel pump arranged between the fuel tank and fuel injectors. The high pressure fuel pump may be coupled to the direct injection system upstream of a fuel rail to raise a pressure of the fuel delivered to the engine cylinders through the direct injectors. A solenoid activated inlet check valve, or spill valve, may be coupled upstream of the high pressure pump to regulate fuel flow into the pump compression chamber. However, when the solenoid activated inlet check valve of the high pressure fuel pump is de-energized, such as when no direct injection of fuel is requested, pump durability may be affected. Specifically, the lubrication and cooling of the pump may be reduced while the high pressure pump is not operated, thereby leading to pump degradation. Pump degradation may be manifested through wear in the interface between the pump piston and bore of the pump. The wear may cause an increase in a gap width between the piston and bore, thereby allowing an increased amount of fuel to flow through that gap compared to a normal amount of leaked fuel. The lost fuel may lead to inefficiencies in the high pressure pump as well as degraded pump and/or engine performance. Various approaches have been developed to detect bore wear that may cause excess fuel leakage through the-piston bore interface.
In one approach to detect leaking fuel from a high pressure pump, shown by Ilhoshiin et al. in U.S. Pat. No. 7,556,023, diagnosis of fuel leakage past a plunger (cylinder) of a high pressure pump is performed by a leak calculation based on a number of factors. The number of factors includes a cam angle signal, crank angle signal, water temperature signal, fuel temperature signal, and fuel pressure signal. The leak calculation calculates a leak amount that is also used to calculate a homo-elasticity coefficient of the fuel. The leak calculation also includes a viscosity coefficient that varies with the fuel temperature.
However, the inventors herein have identified potential issues with the approach of U.S. Pat. No. 7,556,023. First, the leak calculation depends on accurate readings from a large number of sensors, such as various temperatures sensors, pressure sensors, and angle sensors. If one or more sensors were to output an inaccurate value, then the leak calculation may incorrectly diagnose fuel leaking from the plunger. Furthermore, the leak calculation may not be sufficiently calibrated for expected changes in pump operation, such as those due to component wear and aging. As a result, there may be conditions where a leak is erroneously detected even though the change in pump operation is due to normal pump wear. Finally, the leak calculation only provides the diagnosis of any leak, where in many pump systems less than a threshold amount of leakage may be beneficial to pump lubrication, also referred to as normal or necessary leakage. The calculation cannot distinguish between necessary and excessive fuel leakage.
Thus in one example, the above issues may be at least partially addressed by a method, comprising: while an engine is at an idling speed: increasing pressure in a direct injection fuel rail of the engine to a threshold fuel rail pressure; computing a target pump rate of a high pressure fuel pump based on a pump performance model; computing a fuel injection rate; comparing the target pump rate and the fuel injection rate; and issuing a piston-bore interface leak result based on the comparison. In this way, the method for detecting piston bore wear may be continuously performed on-board a vehicle during conditions when the engine is idling. As described herein, the pump performance model may be calibrated based on a number of factors that affect the amount of fuel pumped from the high pressure pump, thereby improving the reliability of results generated via the model. Furthermore, the pump performance model may be compared to test data of an actual high pressure pump so that the model can be verified for its accuracy. The detection method may also be able to achieve high accuracy while relying on fewer sensors, providing component reduction benefits. In addition, the pump performance model may be periodically updated to reflect an aged high pressure pump that may perform differently than a new pump, allowing for variations in pump operation arising from common component wear and tear to be better compensated for. Finally, the detection method may better distinguish between normal and abnormal fuel leakage of the high pressure pump.
The pump performance model may be based on a number of factors, including fuel loss due to bulk modulus of the fuel and a dead volume of a compression chamber of the high pressure pump, a normal fuel leak of the pump, and a miscellaneous cause which may incorporate a number of various fuel loss contributions. The pump performance model may be graphically or numerically compared to a mapped high pressure pump to verify the accuracy of the pump model. Since the model may incorporate a normal amount of leaked fuel (which may enhance pump lubrication such as when high pressure pump operation is not requested), the aforementioned detection method may be configured to let an operator know of an abnormal fuel leakage. For example, an abnormal fuel leakage may be caused by wear between the piston and bore of the high pressure pump. By improving the accuracy and reliability of pump leak detection, pump performance is improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.